Lithographic apparatus and device manufacturing method

ABSTRACT

A system to recycle immersion fluid in an immersion fluid lithographic apparatus is described. A recycling path comprising a plurality of parallel paths, each of which has its own parallel liquid treatment unit optimized to treat fluid which is directed through it, is disclosed.

FIELD

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate using a liquidconfinement system (the substrate generally has a larger surface areathan the final element of the projection system). One way which has beenproposed to arrange for this is disclosed in PCT patent applicationpublication no. WO 99/49504, hereby incorporated in its entirety byreference. As illustrated in FIGS. 2 and 3, liquid is supplied by atleast one inlet IN onto the substrate, preferably along the direction ofmovement of the substrate relative to the final element, and is removedby at least one outlet OUT after having passed under the projectionsystem. That is, as the substrate is scanned beneath the element in a −Xdirection, liquid is supplied at the +X side of the element and taken upat the −X side. FIG. 2 shows the arrangement schematically in whichliquid is supplied via inlet IN and is taken up on the other side of theelement by outlet OUT which is connected to a low pressure source. Inthe illustration of FIG. 2 the liquid is supplied along the direction ofmovement of the substrate relative to the final element, though thisdoes not need to be the case. Various orientations and numbers of in-and out-lets positioned around the final element are possible, oneexample is illustrated in FIG. 3 in which four sets of an inlet with anoutlet on either side are provided in a regular pattern around the finalelement.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

Another immersion lithography solution with a localized liquid supplysystem solution which has been proposed is to provide the liquid supplysystem with a barrier member which extends along at least a part of aboundary of the space between the final element of the projection systemand the substrate table. Such a solution is illustrated in FIG. 5. Thebarrier member is substantially stationary relative to the projectionsystem in the XY plane though there may be some relative movement in theZ direction (in the direction of the optical axis). In an embodiment, aseal is formed between the barrier member and the surface of thesubstrate and may be a contactless seal such as a gas seal.

The barrier member 12 at least partly contains liquid in the space 11between a final element of the projection system PL and the substrate W.A contactless seal 16 to the substrate may be formed around the imagefield of the projection system so that liquid is confined within thespace between the substrate surface and the final element of theprojection system. The space is at least partly formed by the barriermember 12 positioned below and surrounding the final element of theprojection system PL. Liquid is brought into the space below theprojection system and within the barrier member 12 by liquid inlet 13and may be removed by liquid outlet 13. The barrier member 12 may extenda little above the final element of the projection system and the liquidlevel rises above the final element so that a buffer of liquid isprovided. The barrier member 12 has an inner periphery that at the upperend, in an embodiment, closely conforms to the shape of the projectionsystem or the final element thereof and may, e.g., be round. At thebottom, the inner periphery closely conforms to the shape of the imagefield, e.g., rectangular though this need not be the case.

The liquid is contained in the space 11 by a gas seal 16 which, duringuse, is formed between the bottom of the barrier member 12 and thesurface of the substrate W. The gas seal is formed by gas, e.g. air orsynthetic air but, in an embodiment, N₂ or another inert gas, providedunder pressure via inlet 15 to the gap between barrier member 12 andsubstrate and extracted via outlet 14. The overpressure on the gas inlet15, vacuum level on the outlet 14 and geometry of the gap are arrangedso that there is a high-velocity gas flow inwards that confines theliquid. Those inlets/outlets may be annular grooves which surround thespace 11 and the flow of gas 16 is effective to contain the liquid inthe space 11. Such a system is disclosed in United States patentapplication publication no. US 2004-0207824, hereby incorporated in itsentirety by reference.

In European patent application publication no. EP 1420300 and UnitedStates patent application publication no. US 2004-0136494, each herebyincorporated in their entirety by reference, the idea of a twin or dualstage immersion lithography apparatus is disclosed. Such an apparatus isprovided with two tables for supporting a substrate. Levelingmeasurements are carried out with a table at a first position, withoutimmersion liquid, and exposure is carried out with a table at a secondposition, where immersion liquid is present. Alternatively, theapparatus has only one table.

Early immersion lithographic machines have used water as the liquidbetween the projection system and the substrate. Water has a refractiveindex of about 1.4 and is relatively inexpensive. The next generation oflithographic immersion apparatus will use a liquid with a refractiveindex higher than that of water. Unfortunately the candidate liquids arenot as abundant as water and are therefore more expensive. Furthermorethey tend to be harmful to the environment.

SUMMARY

It is desirable, for example, to provide a lithographic apparatus inwhich steps are taken to overcome the otherwise prohibitive cost and/orenvironmental difficulty of using a high refractive index fluid.

According to an aspect of the invention, there is provided alithographic apparatus comprising:

a projection system configured to project a patterned radiation beamonto a target portion of a substrate;

a liquid supply system configured to provide a liquid to a space betweenthe projection system and a substrate; and

a recycling system configured to collect liquid leaving the liquidsupply system and to re-provide the liquid to the liquid supply system,the recycling system comprising two parallel liquid treatment unitsconfigured to treat the liquid, the parallel liquid treatment unitsarranged to treat different liquid such that there are two recyclingpaths for liquid from the liquid supply system through the recyclingsystem back to the liquid supply system.

According to an aspect of the invention, there is provided an immersionlithographic apparatus configured to project a patterned beam ofradiation through a liquid onto a substrate, the apparatus comprising aliquid circuit around which the liquid is configured to flow, the liquidcircuit comprising some parts common to all liquid flow and some partscomprising separate parallel liquid flow paths, wherein at least some ofthe separate parallel liquid flow paths have a liquid treatment unitthrough which liquid in a respective path must pass and wherein theliquid treatment units of different paths are configured to treat liquidpassing through them differently.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising:

using a projection system to project a patterned beam of radiation ontoa substrate through liquid provided to a space between the projectionsystem and the substrate;

removing liquid from the space and treating it in one of several ways inaccordance with how it was removed from the space, in accordance withwhether or not the patterned beam of radiation had passed through it, orboth; and

re-providing at least some of the treated liquid to the space.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts a liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts, in cross-section, another liquid supply system for usein a lithographic projection apparatus;

FIG. 6 depicts, in cross-section, a further type of liquid supply systemfor use in a lithographic projection apparatus;

FIG. 7 illustrates schematically a first embodiment of the presentinvention;

FIG. 8 illustrates schematically a second embodiment of the presentinvention;

FIG. 9 illustrates schematically a third embodiment of the presentinvention;

FIG. 10 illustrates schematically a fourth embodiment of the presentinvention; and

FIG. 11 illustrates schematically a fifth embodiment of the presentinvention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam B (e.g. UV radiation or DUV radiation);    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate in accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PS configured to project a pattern imparted to the radiation        beam B by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more support structures). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AM for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may-berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless-lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Although one or more embodiments will be described relating to animmersion liquid other than water, one or more embodiments of thepresent invention is equally applicable to water. One or moreembodiments of the present invention are particularly suited to animmersion liquid other than water such as one or more of the nextgeneration higher refractive index liquids. These fluids are most likelyto be hydrocarbon fluids such as Decaline. Candidate fluids includeIF131 and WF132 produced by Dupont, HIL-1 and HIL-2 produced by JSR orDelphi produced by Mitsui. Other candidates are mixtures of fluids withnano-particles suspended in them or acids such as phosphoric acids.Because of their high cost, the recycling of high refractive indexliquids in an immersion lithographic apparatus is likely to be moreattractive than the recycling of water.

As will be described with reference to FIG. 6, it will become clearthat, in an immersion lithographic apparatus, immersion liquid which isremoved from a space between the projection system PS and the substrate(where it is at least partly contained by a liquid supply system IH) canbe removed through several different paths. Depending upon the paththrough which the immersion liquid is removed from the space, it isadvantageous to treat that immersion liquid before recycling it backinto the space on an individual basis according to the path it hasfollowed. This is because the path it has followed determines the likelycontaminants within it so that liquid purification can be customized tothose particular contaminants, for example. As well as immersion liquidbeing extracted through the liquid supply system (often in the form of abarrier member 12), immersion liquid may also or alternatively beremoved through the substrate table WT, in particular by removal ofliquid which seeps into a gap between the edge of a substrate W and thesubstrate table WT.

FIG. 6 illustrates a barrier member 12 which is part of a liquid supplysystem IH. The barrier member 12 extends around the periphery of thefinal element of the projection system PS such that the barrier member(which is sometimes called a seal member) is, for example, substantiallyannular in overall shape.

The function of the barrier member 12 is to at least partly maintain orconfine liquid in the space between the projection system PS and thesubstrate W so that the projection beam may pass through the liquid. Thetop level of liquid is simply contained by the presence of the barriermember 12 and the level of liquid in the space is maintained such thatthe liquid does not overflow over the top of the barrier member 12. Aseal is provided between the bottom of the barrier member 12 and thesubstrate W. In FIG. 6 the seal is a contactless seal and is made up ofseveral components. Working radially outwardly from the optical axis ofthe projection system PS, there is provided a (optional) flow plate 50which extends into the space (though not into the path of the projectionbeam) which helps maintain parallel flow of the immersion liquid out ofinlet 20 across the space and then out through an outlet (notillustrated) opposite and at the same level as the inlet (so that theimmersion liquid flows across the space between the final element of theprojection system and the substrate). The flow control plate has one ormore through holes 55 in it to reduce the resistance to movement in thedirection of the optical axis of the barrier member 12 relative to theprojection system PS and/or substrate W. Moving radially outwardly alongthe bottom of the barrier member 12 there is then provided an inlet 60which provides a flow of liquid in a direction substantially parallel tothe optical axis towards the substrate. This flow of liquid is used tohelp fill any gaps between the edge of the substrate W and the substratetable WT which supports the substrate. If this gap is not filled withliquid, bubbles may be more likely to be included in the liquid in thespace between the projection system PS and the substrate W when an edgeof the substrate W passes under the barrier member 12. This isundesirable as it can lead to deterioration of the image quality.

Radially outwardly of the inlet 60 is a extractor assembly 70 configuredto extract liquid from between the barrier member 12 and the substrateW. The extractor 70 will be described in more detail below and formspart of the contactless seal which is created between the barrier member12 and the substrate W.

Radially outwardly of the extractor assembly is a recess 80 which isconnected through an outlet 82 to the atmosphere and via an inlet 84 toa low pressure source. Radially outwardly the recess 80 is a gas knife90. An arrangement of the extractor, recess and gas knife is disclosedin detail in United States patent application publication no. US2006-0158627, incorporated-herein its entirety by reference. However, inthat document the arrangement of the extractor assembly is different.

The extractor assembly 70 comprises a liquid removal device or extractoror outlet 100 such as the one disclosed in United States patentapplication publication no. US 2006-0038968, incorporated herein itsentirety by reference. Any type of liquid extractor can be used. In anembodiment, the liquid removal device 100 comprises an outlet which iscovered in a porous material 110 which is used to separate liquid fromgas to enable single-liquid phase liquid extraction. A chamber 120downstream of the porous material 110 is maintained at a slight underpressure and is filled with liquid. The under pressure in the chamber120 is such that the meniscuses formed in the holes of the porousmaterial prevent ambient gas (e.g., air) being drawn into the chamber120 of the liquid removal device 100. However, when the porous material110 comes into contact with liquid there is no meniscus to restrict flowand the liquid can flow freely into the chamber 120 of the liquidremoval device 100. The porous material 110 extends radially inwardlyalong the barrier member 12 (as well as around the space) and its rateof extraction varies according to how much of the porous material 110 iscovered by liquid.

A plate 200 is provided between the liquid removal device 100 and thesubstrate W so that the function of liquid extraction and the functionof meniscus control can be separated from one another and the barriermember 12 can be optimized for each.

The plate 200 is a divider or any other element which has the functionof splitting the space between the liquid removal device 100 and thesubstrate W into two channels, an upper channel 220 and a lower channel230 wherein the upper channel 220 is between the upper surface of theplate 200 and the liquid removal device 100 and the lower channel 230 isbetween the lower surface of the plate 200 and the substrate W. Eachchannel is open, at its radially innermost end, to the space.

An under pressure can be applied in the upper channel 220, rather thanleaving it open to the atmosphere through one or more breathing holes250, e.g., one or more through holes 250. In this way the upper channel220 can be made wider.

Thus, with the plate 200, there are two meniscuses 310, 320. A firstmeniscus 310 is positioned above the plate 200 and extends between theporous material 110 and the top surface-of the plate 200 and a secondmeniscus 320 which is positioned underneath the plate 200 and whichextends between the plate 200 and the substrate W. In this way, forexample, the extractor assembly 70 can be configured for control of thefirst meniscus for optimum extraction of liquid and for positionalcontrol of the second meniscus 320 such that the viscous drag length forthe second meniscus 320 is reduced. For example, the characteristics, inparticular of the plate 200, may be optimized to make it energeticallyfavorable for the meniscus 320 to remain adhered to the plate 200 suchthat the scan speed of the substrate W beneath the barrier member 10 canbe increased. Capillary forces acting on the second meniscus 320 areoutwards and are balanced by an under pressure in the liquid adjacentthe meniscus so that the meniscus stays still. Higher loading on themeniscus, for example by viscous drag and inertia, results in a loweringof the contact angle of the meniscus with the surface.

As noted above, one or more breathing holes 250 may be provided at theradially outward most end of the plate 200 such that the first meniscus310 is free to move inwardly and outwardly beneath the porous material110 so that the extraction rate of the liquid removal device 100 canvary according to how much of the porous material 110 is covered byliquid. As illustrated in FIG. 6 the second meniscus 320 is adhered to alower innermost edge of the plate 200. In FIG. 6, the innermost loweredge of the plate 200 is provided with a sharp edge so as to pin thesecond meniscus 320 in place.

Although not specifically illustrated in FIG. 6, the liquid supplysystem has a means for dealing with variations in the level of theliquid. This is so that liquid which builds up between the projectionsystem PS and the barrier member 12 can be dealt with and does notspill. Such a build-up of liquid might occur during relative movement ofthe barrier member 12 to a projection system PS described below. One wayof dealing with this liquid is to provide the barrier member 12 so thatit is very large so that there is hardly any pressure gradient over theperiphery of the barrier member 12 during movement of the barrier member12 relative to the projection system PS. In an alternative or additionalarrangement, liquid may be removed from the top of the barrier member 12using, for example, an extractor such as a single phase extractorsimilar to the extractor 110.

Thus, it can be seen that there are several ways in which immersionliquid is -removed from the space between the final element of theprojection system and the substrate. These include immersion liquidwhich flows across the space out of inlet 20 and into an outlet oppositethe inlet 20 (the outlet is not illustrated). This immersion liquid mayor may not be irradiated depending upon when the projection beam PB isactivated. Immersion liquid is removed by the extractor 70 and thisimmersion liquid is likely to be extracted as a single phase. Otherimmersion liquid which escapes the extractor 70 could be collected bythe recess 80 and gas (or fluid-inert gas) knife 90 combination. Anysuch immersion liquid extracted is likely to be a combination of liquidand gas. Finally, liquid is also likely to be removed from the spacethrough the substrate table WS from between the edge of the substrate Wand the substrate table WS. This is also likely to have a high amount ofgas. Liquid which has been in contact with a top surface of thesubstrate (i.e. the resist) may also be contaminated by leaching so thatliquid may be best treated in a particular way different to otherliquid, as described below.

An embodiment of the present invention is directed to treating at leasttwo of the sources of immersion liquid separately in a recycling path orcircuit. Different sources have different levels of contamination andthe more contamination, the more difficult and expensive recyclingbecomes.

One or more embodiments of the invention is applicable to any type ofliquid supply system IH. In the below embodiments, the liquid supplysystem is assumed to have three main types of liquid removed. These aresingle phase immersion liquid which has been in contact with the liquidsupply system and which may or may not have been irradiated; two phaseimmersion liquid which has been in contact with the liquid supply system(i.e. immersion liquid extracted by a gas knife extractor); andimmersion liquid which has been in contact with the substrate table WSand is likely to be two phase. In the Figures these flows are labeled1006, 1004 and 1002 respectively.

One or more aspects or features of one or more embodiments or examplesof the present invention may be used or combined with one or more otherembodiments or examples of the present invention.

Embodiment 1

A first embodiment will be described with reference to FIG. 7. In FIG. 7the liquid supply system IH is illustrated schematically as is thesubstrate table WT on which the substrate W is supported. The solidarrows show the various flow paths of immersion liquid in the liquidcircuit 1000. As can be seen, liquid is prepared in a liquid preparationmodule 1150 and supplied through line 1050 to the liquid supply systemIH. The liquid supply system IH fills the space between the projectionsystem PB and the substrate W with the liquid.

In this and other embodiments, three types of immersion liquid are shownas being removed from that space though there may be less or more thanthree. The three types of liquid are the liquid 1002 which is extractedfrom the space through the substrate table WT, the liquid 1004 which isextracted from the space through, e.g., a gas knife extractor and theliquid 1006 which is extracted through, e.g., an outlet in the side ofthe barrier member 12. Each of these types of liquid has its ownparallel liquid treatment units 1102, 1104, 1106 in the recyclingsystem. The parallel liquid treatment units 1102, 1104, 1106 areoptimized to treat the respective flow of immersion liquid for the typesof contaminants likely to be present.

Thus, the parallel liquid treatment unit 1102, which treats theimmersion liquid from the substrate table WT, has a degassing unit todegas the immersion liquid which passes through it, and has a purifierto for purify the immersion liquid. The purifier will be optimized topurify immersion liquid which has come into contact with the substratetable WT. The parallel liquid treatment unit 1102 also has one or moreparticle filters which are optimized to extract particles likely to havecontaminated the immersion liquid in the substrate table WT. In theparallel liquid treatment units, the particle filter(s) is for fairlycoarse particles.

Equally the parallel liquid treatment unit 1104 for the liquid 1004,which exits through, for example, the gas knife extractor of the liquidsupply system, has a degassing unit, a purifier and one or more particlefilters. The purifier and one or more particle filters of the parallelliquid treatment unit 1104 will be optimized for immersion liquid whichhas been in contact with the liquid supply system IH (e.g., barriermember 12). The unit 1104 will be optimized to remove particles andpurify immersion liquid which has been acted on by, for example, a gasknife which may result in its own particular type of impurities andparticles.

As will be appreciated, the liquid 1002 may also have been in contactwith the liquid supply system IH and the liquid 1004 may have been incontact with the top surface of the substrate table WT.

Finally, the liquid 1006, which has simply passed across the space andis therefore likely to be removed from the space as a single phase, willbe treated by the liquid treatment unit 1106 which may not comprise adegassing unit (because there will likely be no gas in the liquidbecause there would have been no opportunity for gas to be introducedinto that liquid) but will comprise a purifier and one or more particlefilters optimized to remove particles which are likely to exist in theliquid supply system.

The three flows are illustrative only. There may be other flows, forexample a single phase flow extracted through an extractor between theliquid supply system IH and the substrate W, such as extractor 70.

The flows of liquid out of the parallel liquid treatment units 1102,1104, 1106 are combined by a fluid cycling integrator 1110 and suppliedfurther as flow 1010 to a container or buffer 1120 where the liquid isstored until it is used by the fluid preparation unit 1150. The fluidpreparation unit 1150 may itself comprise several units to treat theliquid prior to it being supplied to the liquid supply system IH. Thefluid preparation unit 1150 can be seen as a serial liquid treatmentunit in that all of the recycled immersion liquid will pass through itfrom the container 1120 via flow 1020. The fluid preparation unit 1150could contain a degassing unit, a temperature control unit, a flowcontrol unit and a refractive index control unit. In the embodimentillustrated in FIG. 7, the fluid preparation unit 1150 has a fineparticle filter unit for final filtration after the one or more coarsefilters of the parallel liquid treatment units 1102, 1104, 1106. Ofcourse any of these parts of the fluid preparation unit 1150 could bepositioned separately in the flow paths 1010 or 1020.

Elements of the fluid preparation unit 1150 can be controlled in afeed-back manner based on measurements taken at the substrate table WTusing sensors 1212 and 1214. Sensor 1212 could, for example, be awavefront sensor and sensor 1214 could be an intensity (absorption)sensor. Based on the measurement results of these sensors, the fluidpreparation unit 1150 and the rest of the lithographic apparatus couldbe controlled to achieve the correct wavefront-position and dose. Thisis achieved through control signals 2212 and 2214. The final preparationunit 1150 could vary how the immersion fluid is prepared prior toentering the liquid supplied system IH and thereby control therefractive index (e.g. by temperature variation). One or both of thosesensors could also be used in determining when it is necessary to renewthe immersion liquid in the circuit 1000. Obviously it is desirable toensure that the absorption remains below a pre-determined maximumacceptable level and that the refractive index remains stable and if notthat the refractive index is known so that the necessary opticalcorrections can be made. Alternatively or additionally, there could be aregular program in place for the periodical replacement of liquid in thecircuit 1000.

Parts of the circuit 1000 could be supplied with the main bulk of theimmersion lithographic apparatus and other parts, in particular theparallel treatment units, could be provided as a separate unit from thebulk of the immersion lithographic apparatus.

The apparatus of this and other embodiments may be part of a closedsystem or a partially closed system. This is in contrast to an opensystem in which immersion liquid which is removed from the lithographicapparatus is either disposed or is re-worked offline and laterre-supplied to the lithographic apparatus. In a closed system the liquidin the apparatus is continually recycled and the liquid is notreplenished in use with fresh liquid. It may be necessary to include twopaths through which the fluid may be recycled in a closed system (aswell as in a partially closed system) in case for some reason a part ofthe recycling system becomes inoperative. Thus, effectively there wouldbe one or more valves to divert the liquid from, for example, one ormore of the liquid treatment units 1102, 1104, 1106, fluid cyclingintegrator 1110, container 1120 and fluid preparation unit 1150 to aseparate circuit comprising the same components. The valve(s) may bepart of one or more of those devices or in the flow path before or afterone or more of those devices as appropriate. In a partially closedsystem, fresh liquid can be added (for example to the container 1120during operation of the recycling system). Liquid exiting the liquidsupply IH or substrate table WT could be diverted to be disposed of orto be re-worked offline prior to being re-supplied to the container1120. Using this system new immersion liquid can be added into thecircuit 1000 without interruption of the flow of immersion liquid sothat new immersion liquid can be added without any downtime of the wholeapparatus.

Embodiment 2

A second embodiment is illustrated in FIG. 8 and is the same as thefirst embodiment except as is described below.

In the second embodiment, the apparatus has a further control signal2115 from the fluid preparation unit 1150 to a pressure control unit1115. This ensures that the fluid preparation unit 1150 receivesimmersion liquid at the correct rate. This arrangement is particularlyuseful if the fluid recycling integrator 1110 and the parallel treatmentunits 1102, 1104, 1106 are part of a separate machine to the remainderof the circuit 1000.

Furthermore, two sensors 1216, 1218 are provided in the path 1020 fromthe container 1120 to the fluid preparation unit 1150. These sensorsmeasure the refractive index of the immersion liquid directly and/or theabsorption of the immersion liquid.

The outputs of the sensors 2216, 2218 are provided to the fluidrecycling integrator (and/or one or more of the parallel treatment units1102, 1104, 1106) so that any necessary adjustment can be made directlyto reach the desired refractive index and/or absorption of the immersionliquid entering the fluid preparation unit 1150. This extra controlprior to entry of the immersion liquid into the fluid preparation unit1150 may result in increased control of the properties of the immersionliquid entering the liquid supply system IH.

Embodiment 3

A third embodiment is illustrated in FIG. 9 and is the same as the firstor second embodiment except as is described below.

In order to ease splitting of the parallel treatment units 1102, 1104,1106 from the remainder of the lithographic apparatus, in the thirdembodiment the parallel treatment units 1102, 1104, used to treatimmersion liquid which may have had gas incorporated in it, do not havedegassing units. Instead, separate degassing units 1014, 1012 areprovided in the immersion liquid paths 1002, 1004 prior to thoseimmersion liquid paths reaching their respective parallel treatmentunits 1102, 1104. In this way the degassing units, which can be quitecomplicated, can be formed as part of the lithographic apparatus therebyeasing the splitting up of the unit into two parts.

Embodiment 4

A fourth embodiment is illustrated in FIG. 10. The fourth embodiment isthe same as the first embodiment except as described below.

In the fourth embodiment, a fourth parallel treatment unit 1108 isprovided. The flow path 1006 which contains single phase immersionliquid which has passed across the space is either directed through apath 1016 to parallel treatment unit 1106 or alternatively directedthrough path 1026 to parallel treatment unit 1108. The destination ofimmersion liquid in flow path 1006 is chosen by a valve 1101 which iscontrolled by a signal 2160 from a dose control system 1160 whichperforms a calculation to establish whether immersion liquid in path1006 upstream of the valve 1101 has been irradiated or not. If theimmersion liquid has been irradiated, the valve is switched so that theimmersion liquid passes through path 1026 to parallel treatment unit1108 and such that if the immersion liquid upstream of the valve 1101has not been irradiated that it passes through path 1016 to paralleltreatment unit 1106. In this way, parallel treatment units 1106 and 1108can be optimized for the treatment, on the one hand, of immersion liquidwhich has not been irradiated (which may need very little, if any,treatment) and on the other hand for treatment of immersion liquid whichhas been irradiated.

Embodiment 5

A fifth embodiment is illustrated in FIG. 11. The fifth embodiment isthe same as the fourth embodiment except as described below.

The fifth embodiment is optimized in order to recycle the immersionliquid which passes through the liquid supply system during idle time ofthe apparatus. Idle time is when liquid is flowing through the liquidsupply system IH but there is no irradiation of a substrate and thesubstrate is not being scanned under the liquid supply system IH. Thesystem is ready to start imaging and exposing. In this case a signal2180 is provided by a system controller 1180 to a valve 1171 whichdirects immersion fluid from the liquid supply system IH to a buffer1170 and thereby to the container 1120 without passing through the anyof the parallel liquid treatment units 1102, 1004, 1106, 1108. In thisway unnecessary use of the parallel liquid treatment units is avoided.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm). The term“lens”, where the context allows, may refer to any one or combination ofvarious types of optical components, including refractive and reflectiveoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above and whether the immersion liquid is provided in the formof a bath or only on a localized surface area of the substrate. A liquidsupply system as contemplated herein should be broadly construed. Incertain embodiments, it may be a mechanism or combination of structuresthat provides a liquid to a space between the projection system and thesubstrate and/or substrate table. It may comprise a combination of oneor more structures, one or more liquid inlets, one or more gas inlets,one or more gas outlets, and/or one or more liquid outlets that provideliquid to the space. In an embodiment, a surface of the space may be aportion of the substrate and/or substrate table, or a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.The liquid supply system may optionally further include one or moreelements to control the position, quantity, quality, shape, flow rate orany other features of the liquid.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A lithographic apparatus, comprising: a projection system configuredto project a patterned radiation beam onto a target portion of asubstrate; a liquid supply system configured to provide a liquid to aspace between the projection system and a substrate; and a recyclingsystem configured to collect liquid leaving the liquid supply system andto re-provide the liquid to the liquid supply system, the recyclingsystem comprising two parallel liquid treatment units configured totreat the liquid, the parallel liquid treatment units arranged to treatdifferent liquid such that there are two recycling paths for liquid fromthe liquid supply system through the recycling system back to the liquidsupply system, wherein the two parallel liquid treatment units areconfigured to apply different treatments to the respective liquid suchthat, in use, one of the two parallel liquid treatment units treats alevel or type of contaminant or both in the liquid that is differentfrom a level or type of contaminant or both in the liquid treated by theother one of the two parallel liquid treatment units.
 2. Thelithographic apparatus of claim 1, wherein each of the parallel liquidtreatment units are configured to treat liquid from a different source.3. The lithographic apparatus of claim 1, further comprising a serialliquid treatment unit configured to treat liquid before entering orafter leaving at least one of the parallel liquid treatment units. 4.The lithographic apparatus of claim 3, wherein the serial liquidtreatment unit comprises one unit selected or a combination of unitsselected from a list comprising: a degassing unit configured to degasliquid which passes through the degassing unit, a temperature controlunit configured to regulate a temperature of liquid passing through thetemperature control unit, an index control unit configured to controlthe refractive index of liquid passing through the index control unit, aparticle filter unit configured to filter out particles from liquidpassing through the particle filter unit, or a flow control unitconfigured to regulate a flow rate of liquid through the flow controlunit.
 5. The lithographic apparatus of claim 1, wherein each of theparallel treatment units comprises one unit selected or a combination ofunits selected from a list comprising: a degassing unit configured todegas liquid which passes through the degassing unit, a temperaturecontrol unit configured to regulate a temperature of liquid passingthrough the temperature control unit, an index control unit configuredto control the refractive index of liquid passing through the indexcontrol unit, or a particle filter unit configured to filter outparticles from liquid passing through the particle filter unit.
 6. Thelithographic apparatus of claim 1, wherein there is a separate recyclingpath for one or a combination selected from the following: liquid whichhas been exposed to radiation from the projection system, liquid whichhas passed through a substrate table on which the substrate is to besupported, liquid which has passed through the liquid supply system,liquid which has interacted with a gas knife, or liquid which has notbeen exposed to radiation from the projection system, not been exposedto a top surface of the substrate, or both.
 7. The lithographicapparatus of claim 1, further comprising a valve configured to switch aflow path from a path through one of the parallel liquid treatment unitsinstead to through another of the parallel liquid treatment units. 8.The lithographic apparatus of claim 7, further comprising a flowcontroller configured to control the valve according to a result of acalculation as to whether or not liquid upstream of the valve has beenirradiated by radiation from the projection system.
 9. The lithographicapparatus of claim 1, further comprising a sensor configured to measurea quality of the liquid.
 10. The lithographic apparatus of claim 9,wherein the sensor is configured to measure (i) an intensity of aradiation beam passing through the liquid, or (ii) absorption of theliquid, or (iii) the refractive index of the liquid, or (iv) a wavefrontposition error in a radiation beam passing through the liquid, or (v)any combination of (i)-(iv).
 11. The lithographic apparatus of claim 9,wherein (i) an output of the sensor is used to adjust a parameter of therecycling system to achieve a desired property of the liquid, or (ii) anoutput of the sensor is used to adjust an imaging parameter of thelithographic apparatus, or (iii) both (i) and (ii).
 12. The lithographicapparatus of claim 9, further comprising a liquid controller configuredto control (i) at least one of the parallel liquid treatment units, (ii)a serial liquid treatment unit configured to treat liquid beforeentering or after leaving one or more of the parallel liquid treatmentunits, or (iii) a fluid recycling integrator configured to integrateseparate liquid flows into one, or (iv) any combination of (i)-(iii), onthe basis of an output of the sensor so as to control the quality of theliquid.
 13. The lithographic apparatus of claim 1, wherein, in use, theone of the two parallel liquid treatment units imparts a change to thelevel or type of contaminant or both in the liquid that is differentfrom a change to the level or type of contaminant or both in the liquidimparted by the other one of the two parallel liquid treatment units.14. An immersion lithographic apparatus configured to project apatterned beam of radiation through a liquid onto a substrate, theapparatus comprising a liquid circuit around which the liquid isconfigured to flow, the liquid circuit comprising some parts common toall liquid flow and some parts comprising separate parallel liquid flowpaths, wherein at least some of the separate parallel liquid flow pathshave a liquid treatment unit through which liquid in a respective pathmust pass and wherein the liquid treatment units of different paths areconfigured to treat liquid passing through them differently such that,in use, one of the liquid treatment units treats a level or type ofcontaminant or both in the liquid that is different from a level or typeof contaminant or both in the liquid treated by another one of theliquid treatment units.
 15. The lithographic apparatus of claim 14,wherein each of the liquid treatment units are configured to treatliquid from a different source.
 16. The lithographic apparatus of claim14, wherein each of the liquid treatment units comprises one unitselected or a combination of units selected from a list comprising: adegassing unit configured to degas liquid which passes through thedegassing unit, a temperature control unit configured to regulate atemperature of liquid passing through the temperature control unit, anindex control unit configured to control the refractive index of liquidpassing through the index control unit, or a particle filter unitconfigured to filter out particles from liquid passing through theparticle filter unit.
 17. The lithographic apparatus of claim 14,wherein there is a separate liquid flow path for one or a combinationselected from the following: liquid which has been exposed to radiationfrom the projection system, liquid which has passed through a substratetable on which the substrate is to be supported, liquid which has passedthrough a liquid supply system configured to supply the liquid to aspace between the projection system and the substrate, liquid which hasinteracted with a gas knife, or liquid which has not been exposed toradiation from the projection system, not been exposed to a top surfaceof the substrate, or both.
 18. The lithographic apparatus of claim 14,further comprising a sensor configured to measure a quality of theliquid.
 19. The lithographic apparatus of claim 18, wherein (i) anoutput of the sensor is used to adjust a parameter of the liquid circuitto achieve a desired property of the liquid, or (ii) an output of thesensor is used to adjust an imaging parameter of the lithographicapparatus, or (iii) both (i) and (ii).
 20. The lithographic apparatus ofclaim 18, further comprising a liquid controller configured to control(i) at least one of the liquid treatment units, (ii) a serial liquidtreatment unit configured to treat liquid before entering or afterleaving one or more of the liquid treatment units, or (iii) a fluidrecycling integrator configured to integrate separate liquid flows intoone, or (iv) any combination of (i)-(iii), on the basis of an output ofthe sensor so as to control the quality of the liquid.
 21. Thelithographic apparatus of claim 14, wherein, in use, the one of theliquid treatment units imparts a change to the level or type ofcontaminant or both in the liquid that is different from a change to thelevel or type of contaminant or both in the liquid imparted by the otherone of the liquid treatment units.
 22. A device manufacturing methodcomprising: using a projection system to project a patterned beam ofradiation onto a substrate through liquid provided to a space betweenthe projection system and the substrate; removing liquid from the spaceand treating a level or type of contaminant or both in the liquid in oneof several ways in accordance with how the liquid was removed from thespace, in accordance with whether or not the patterned beam of radiationhad passed through the liquid, or both; and re-providing at least someof the treated liquid to the space.
 23. The method of claim 22, whereinthe treating includes imparting a change to the level or type ofcontaminant or both in the liquid.